The present invention relates to an improved apparatus for driving rollers in a roller hearth kiln and more particularly to a combination of connection means for connecting a ceramic roller with a metallic drive shaft.
Various types of roller hearth kilns are known which are adapt to sinter articles while being conveyed on a number of ceramic rollers arranged along a tunnel of the kiln. The rollers may be replaced by new rollers when they wear away or are damaged. The rollers also must be periodically demounted and cleaned when glaze on the articles is unintentionally applied to the rollers. On replacing or cleaning, the operation of the kiln must be stopped. If it takes a long time to demount the rollers from the kiln, the productivity will be reduced.
Japanese Utility Model Publication Sho 64-4072 discloses a modification of a roller hearth kiln. FIGS. 10, 11 and 12 in the accompanying drawings show such an apparatus for driving rollers. The apparatus comprises a number of rollers 2 extending from opposite sides of the tunnel through the walls 1 of the kiln. A rotary drive device 3 holds each of the rollers at one end and a support device 4 rotatably supports each of the rollers 2 at the other end. Each of the rollers 2 is kept in a spring 5 which is wound therearound at one end 2a. The outer periphery of the spring 5 is pressed by a plurality of pawls 7, such that the roller 2 is connected with a drive shaft 10 through a cylinder 8 via the spring 5. The drive shaft 10 is rotatably supported by a support frame 11 and receives a drive power from a source of drive through a sprocket 12. The driven end 2b of the roller 2 is supported, in two-point linear contact as shown in FIGS. 11 and 12, by a pair of receiver rollers 9 which are mounted on brackets 17 attached at frames 18 on the side hearth walls 1a. When the drive power is transmitted to the rollers 2 to rotate them, the receiver rollers 9 are also rotated.
In the prior art driving mechanism as mentioned above, each of the rollers 2 may be removed from the connection structure to draw the roller 2 in the right-hand direction as viewed in FIG. 10. At this time, the spring 5 wound around the roller end 2a will be passed throught the hearth at high temperature. Thus, the spring 5 will reduce its resiliency and may be accidentally removed out of the roller 2.
If there is any trouble in the hearth, the rollers might be driven in the reverse direction to convey articles toward the inlet side of the hearth. In such a case, a frictional force will exist between each of the roller ends 2aand the corresponding spring 5, and will loosen the winding of the spring 5 to raise the pawls 7 into its opened state. Thus, the pawls 7 might be disengaged from the corresponding roller 2.
In the prior art, the rollers 2 made of ceramics were produced with an increased dispersion in external diameter due to the manufacturing process. Such an increased dispersion could produce a slippage between each of the rollers 2 and the corresponding receiver roller 9 which would make the speed of the roller irregular. Therefore, the conveyance of articles is irregular. For example, a manufacturing tolerance equal to .+-.one millimeter may exist when a roller has its external diameter equal to 25 mm. A difference equal to six millimeters in distance of conveyance may exist between each adjacent rollers through one complete revolution when a plurality of such rollers are used. This results in irregularity of conveyance due to the slippage between the rollers 2. Furthermore, either of the ceramic roller 2 and the metallic receiver roller 9 is subject to being worn away since the rollers have a difference in hardness. For example, if the external diameters of adjacent rollers 2, as shown in FIG. 11, are respectively equal to 24 mm and 26 mm and the external diameter of the respective receiver rollers 9 is equal to 40 mm, a deviation equal to 6 mm will be created between one roller 2 having its external diameter of 26 mm and the corresponding receiver roller 9 when the other roller 2 having its external diameter of 24 mm is rotated through one complete revolution. This results in slippage between the rollers which increases wear.